Commingled wells production

[triviaux1]

Hello,

I m working in a field where oil producers are connected to several manifold which are then connected to the processing facilities.

I'm wondering if the network and commingled wells could affect the total production as the production of each individual well is not matching the total production received at the processing facilities production separator

Appreciate your feedback

 

[1503-44]

There could be a number of reasons for inequalities, probably having more to do with differences in wellhead processing equipment and measurement techniques. That might be related to different streams at each well and what types of meters those streams have.

What's the stream analysis and how does the flow diagram look?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[triviaux1]

Thanks for your feedback

At the well head we have multiphase flow meter for continuous well production monitoring and a separator at the processing facilities.

Wells are commingled on two main manifold ( one low pressure manifold and one high pressure manifold).

I assume that the following could be the main contributor :

Constrained due to surface commingling and facility back pressure can have an impact on the total production received at the processing facilities.
Pressure lost or line pressure different from what is normally the production conditions when the well is commingling with the others.

Any thought ?

 

[1503-44]

The meters should all be giving volumes at pressure and temperature adjusted to standard volumes at 1 atmosphere and 20°C. However depending on the actual stream contents, the pressures and temperatures, the same well stream might give you different quantities of gas and liquids at two metering points, if there is any change in pressure and temperature between metering points. Some liquids can turn into gas, or visa versa. Any balance attempt has to be carefully made, considering potential phase changes and compressibility factors of all components in the streams.

And yes, backpressure changes at the wellhead can result in differing quantity of liquids and gases actually being produced from a well, which again depending on the phase of the stream components being produced at any given moment, may cause considerable difference in liquid to gas ratios.

It is probably easier to convert all volumes to mass measurements and try to balance masses of each component passing each meter location but in any case, you need a detailed analysis of all streams to even try to do it.

Are all meters the same type and readings taken at the same frequency?

Depending on how your pipeline works, you can get slugging of liquids for some time, then excess gas flows for awhile too. Those factors can make balancing over short time intervals pretty complicated, if not useless at times. You may not be able to balance daily, but get an average balance over a week or month that is smoother.


--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[triviaux1]

Thanks for your constructive comments and I agree mass comparison shall be more appropriate.

I’m considering the following lab analysis to verify MPFM readings: ( and yes MPFM are all the same type and reading continuously.

Take a pressurized samples on the HP and LP separator for the gas, and analyze up to C12+, to determine any components in the gas, which we want to consider as liquid normally, and can actually ask the lab to consider average multiphase conditions, when determining if entrained liquid in the gas (such as example of nonane which has a boiling point at atmospheric of 151 DegC). It would need to be average multiphase)condition for the wells going to the particular train.

Then I would to consider both temperature and pressure and the lab results on the gas:liquid ratio to determine Gas:Liquid Ratio and Gas:Oil ratios, both on a Mass basis.
This can then be used to verify the multiphase meters by summing the multiphase’s single phases mass totals for gas, oil and water reported by all multiphase meters connected to the train, and then calculating the Gas:Liquid and Gas:Oil (Mass basis) ratios of the total multiphase meters, and comparing directly against the Lab results.
This allow verification that all wells connected to the multiphase meter are as a sum correctly determining split of phases (actually including WaterCut based on the Gas:Liquid Ratio check), but see next check which actually checks water cut.

I could then calculate the watercut on a std volume basis, based on the measured density and the weight percentages from the C36+ liquid phases components, and the water based on its weight percentage and standard density of water to calculate a watercut on a std vol basis, and also perform an actual measurement of watercut using traditional methods. All Multiphase meters connected to the train std volumes totals of oil and water shall be summed to determine an overall watercut for the train, and this verified against the lab results.
this allow verification that all attatched multiphase meter are as a sum correctly determining watercut.
As such with the lab results I can verify 2 of the 3 important things from the multiphase meters – correct determination of GLR and Watercut. Now to the last important thing, the initiating mass total flow of the multiphase meter, we need to now consider the single phase separator meter results, and assume entrained liquids in gas and gas in liquids are not detrimental to the mass results from these meters to more than the expected accuracy of a multiphase meter.

I can also get from the lab analysis the 3-phase emulsion density of the liquid at operating conditions. I suggest by measurement of weight (tared vs final after sample and adjusted for weight of initial nitrogen, argon or whatever was in sample bottle before sample).

. For the gas the initial rate is mass, but again requires the gas composition split to be known, and as such before starting the C12+ analysis should be done, as indeed the C36+ analysis to determine the emulsion density. Once the overall mass totals as obtained from the associated train separators is measured, this can be compared against the sum of all multiphases meter mass totals attatched to the train.
this allow verification that all wells connected to the multiphase meter are as a sum correctly measuring mass.

As such it is clear that its actually the pressurized samples which are fundamental to verification of the multiphase meters, since it checks 2 of the 3 things (GLR and WaterCut). The processing facilities single phase meters performance if OK allows completing the holistic checks, but even if they are not performing or give significantly different results, we can still make determinations of 2 of the 3 fundamentals. However, if multiphase / separator mass rates are consistent, we complete the entire performance.

 

[1503-44]

The standard volumes of liquid and gases that do not change phase between meters can be added directly, liquid to liquid, gas to gas, but those that change phase cannot, so pay particular attention to those that do and especially any gases coming out of solution.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[triviaux1]

Right but if the comparison is done in term of mass for the GLR the change of phase shall not impact the evaluation

 

[1503-44]

Correct. By that I simply mean you must start using the flow data you have. If it's component stream and volumes, then you need to convert whatever volume x stream% to get mass flows of each component to do your calcs. Then, if you have meters reading volumes, you cannot compare the resulting calculated mass flow rates to meter volume flow without converting mass rate back to volume rates. Or visa versa. In any case, the conversions are rather simple for those components that do not change phase.



--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

A field I worked on a few years ago has a similar issue where some of the execs were getting agitated because the volume of liquid measured at the first stage separator at 50 bar was a lot different (more) than the stock tank liquid being exported. Accusations of stealing.

They couldn't understand that liquid at 50C and 50 bar wasn't the same liquid as 20 C and 0 bar. Follow the molecules....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Things like that can make you crazy.
Operating a glycol dehy at 150% will blow a lot of glycol down the pipeline.
They thought someone was making off with it, but security couldn't manage to catch them in the act.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."